I have the original Sonata, but the door size is exactly the same. The difference is that you do not have the pre drilled holes in the top.
I wanted to add a window to mine, so I searched for alot for a window. AS stated above, there is no window available pre-cut for a Sonata that I ever found.
With the handle in the door, it really narrows down the kits that you can get. The fact that you can use the entire height of the door (where I cannot due to the drilled holes), will make it easier to find one that fits though.
Alot of kits come with everything you need, including a cheap cutting tool. Not sure how well the took will work because the steel on the Sonata is fairly thick. I did end up adding a 120mm fan to the door, and just cutting the hole for the fan was a PITA. I ended up buying a Dremel to do the job, and would suggest using one vice any sort of cutter.